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694470273d
snd_seq_oss_readq_put_event() seems to be missing a memory barrier which
might cause the waker to not notice the waiter and miss sending a
wake_up as in the following figure.
snd_seq_oss_readq_put_event snd_seq_oss_readq_wait
------------------------------------------------------------------------
/* wait_event_interruptible_timeout */
/* __wait_event_interruptible_timeout */
/* ___wait_event */
for (;;) { prepare_to_wait_event(&wq, &__wait,
state);
spin_lock_irqsave(&q->lock, flags);
if (waitqueue_active(&q->midi_sleep))
/* The CPU might reorder the test for
the waitqueue up here, before
prior writes complete */
if ((q->qlen>0 || q->head==q->tail)
...
__ret = schedule_timeout(__ret)
if (q->qlen >= q->maxlen - 1) {
memcpy(&q->q[q->tail], ev, sizeof(*ev));
q->tail = (q->tail + 1) % q->maxlen;
q->qlen++;
------------------------------------------------------------------------
There are two other place in sound/core/seq/oss/ which have similar
code. The attached patch removes the call to waitqueue_active() leaving
just wake_up() behind. This fixes the problem because the call to
spin_lock_irqsave() in wake_up() will be an ACQUIRE operation.
I found this issue when I was looking through the linux source code
for places calling waitqueue_active() before wake_up*(), but without
preceding memory barriers, after sending a patch to fix a similar
issue in drivers/tty/n_tty.c (Details about the original issue can be
found here: https://lkml.org/lkml/2015/9/28/849).
Signed-off-by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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|---|---|---|
| .. | ||
| oss | ||
| seq | ||
| compress_offload.c | ||
| control_compat.c | ||
| control.c | ||
| ctljack.c | ||
| device.c | ||
| hrtimer.c | ||
| hwdep_compat.c | ||
| hwdep.c | ||
| info_oss.c | ||
| info.c | ||
| init.c | ||
| isadma.c | ||
| jack.c | ||
| Kconfig | ||
| Makefile | ||
| memalloc.c | ||
| memory.c | ||
| misc.c | ||
| pcm_compat.c | ||
| pcm_dmaengine.c | ||
| pcm_drm_eld.c | ||
| pcm_iec958.c | ||
| pcm_lib.c | ||
| pcm_memory.c | ||
| pcm_misc.c | ||
| pcm_native.c | ||
| pcm_timer.c | ||
| pcm_trace.h | ||
| pcm.c | ||
| rawmidi_compat.c | ||
| rawmidi.c | ||
| rtctimer.c | ||
| sgbuf.c | ||
| sound_oss.c | ||
| sound.c | ||
| timer_compat.c | ||
| timer.c | ||
| vmaster.c | ||